Fuel cell device

ABSTRACT

Fuel cell devices are provided having improved shrinkage properties between the active and non-active structures by modifying the material composition of the non-active structure, having a non-conductive, insulating barrier layer between the active structure and surface conductors that extend over the inactive surrounding support structure, having the width of one or both electrodes progressively change along the length, or having a porous ceramic layer between the anode and fuel passage and between the cathode and air passage. Another fuel cell device is provided having an internal multilayer active structure with electrodes alternating in polarity from top to bottom and external conductors on the top and/or bottom surface with sympathetic polarity to the respective top and bottom electrodes. A fuel cell system is provided with a fuel cell device having an enlarged attachment surface at one or both ends, which resides outside the system&#39;s heat source, insulated therefrom.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 37 C.F.R. §1.78(a)(4), this application claims the benefitof and priority to prior filed Provisional Application Ser. No.61/565,156, filed Nov. 30, 2011, and entitled FUEL CELL DEVICE, which isexpressly incorporated herein by reference.

The present application is related to co-pending U.S. patent applicationSer. No. 12/399,732 filed Mar. 6, 2009, and U.S. patent application Ser.No. 12/607,384 filed Oct. 28, 2009, and each entitled FUEL CELL DEVICEAND SYSTEM, the disclosures of which are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

This invention relates to fuel cell devices and systems, and methods ofmanufacturing the devices, and more particularly, to a solid oxide fuelcell device.

BACKGROUND OF INVENTION

Ceramic tubes have found a use in the manufacture of Solid Oxide FuelCells (SOFCs). There are several types of fuel cells, each offering adifferent mechanism of converting fuel and air to produce electricitywithout combustion. In SOFCs, the barrier layer (the “electrolyte”)between the fuel and the air is a ceramic layer, which allows oxygenatoms to migrate through the layer to complete a chemical reaction.Because ceramic is a poor conductor of oxygen atoms at room temperature,the fuel cell is operated at 700° C. to 1000° C., and the ceramic layeris made as thin as possible.

Early tubular SOFCs were produced by the Westinghouse Corporation usinglong, fairly large diameter, extruded tubes of zirconia ceramic. Typicaltube lengths were several feet long, with tube diameters ranging from ¼inch to ½ inch. A complete structure for a fuel cell typically containedroughly ten tubes. Over time, researchers and industry groups settled ona formula for the zirconia ceramic which contains 8 mol % Y₂O₃, and isreferred to as yttria stabilized zirconia (YSZ). This material is madeby, among others, Tosoh of Japan as product TZ-8Y.

Another method of making SOFCs makes use of flat plates of zirconia,stacked together with other anodes and cathodes, to achieve the fuelcell structure. Compared to the tall, narrow devices envisioned byWestinghouse, these flat plate structures can be cube shaped, 6 to 8inches on an edge, with a clamping mechanism to hold the entire stacktogether.

A still newer method envisions using larger quantities of small diametertubes having very thin walls. The use of thin walled ceramic isimportant in SOFCs because the transfer rate of oxygen ions is limitedby distance and temperature. If a thinner layer of zirconia is used, thefinal device can be operated at a lower temperature while maintainingthe same efficiency. Literature describes the need to make ceramic tubesat 150 μm or less wall thickness.

An SOFC tube is useful as a gas container only. To work it must be usedinside a larger air container. This is bulky. A key challenge of usingtubes is that you must apply both heat and air to the outside of thetube; air to provide the O₂ for the reaction, and heat to accelerate thereaction. Usually, the heat would be applied by burning fuel, so insteadof applying air with 20% O₂ (typical), the air is actually partiallyreduced (partially burned to provide the heat) and this lowers thedriving potential of the cell.

An SOFC tube is also limited in its scalability. To achieve greater kVoutput, more tubes must be added. Each tube is a single electrolytelayer, such that increases are bulky. The solid electrolyte tubetechnology is further limited in terms of achievable electrolytethinness. A thinner electrolyte is more efficient. Electrolyte thicknessof 2 μm or even 1 μm would be optimal for high power, but is verydifficult to achieve in solid electrolyte tubes. It is noted that asingle fuel cell area produces about 0.5 to 1 volt (this is inherent dueto the driving force of the chemical reaction, in the same way that abattery gives off 1.2 volts), but the current, and therefore the power,depend on several factors. Higher current will result from factors thatmake more oxygen ions migrate across the electrolyte in a given time.These factors are higher temperature, thinner electrolyte, and largerarea.

Fuel utilization is a component of the overall efficiency of the fuelcell. Fuel utilization is a term that can describe the percent of fuelthat is converted into electricity. For example, a fuel cell may onlyconvert 50% of its fuel into electricity, with the other 50% exiting thecell un-used. Ideally, the fuel utilization of a fuel cell would be100%, so that no fuel is wasted. Practically, however, total efficiencywould be less than 100%, even if fuel utilization was 100%, because ofvarious other inefficiencies and system losses.

A challenge for fuel utilization at the anode is to move molecules offuel into the pores of the anode. Another challenge is to move the wasteproducts, i.e., water and CO₂ molecules, out of the pores of the anode.If the pores are too small, then the flow of fuel inward andwaste-products outward will be too slow to allow high fuel utilization.

An analogous condition exists for the cathode. Because air is only 20%oxygen, and has 80% nitrogen, there is a challenge to move oxygen intothe pores and N₂ out of the pores. Collectively, utilization of the fueland air input to the device may be referred to as “gas utilization.”

One problem for gas utilization is that air and fuel can pass throughthe flow paths past the porous anodes and cathodes without the moleculesever entering the pores. The “path of least resistance” would lead amolecule to bypass the most important part of the fuel cell.

Additionally, if the gas molecules can't get into and out of the anodeand cathode, then the fuel cell will not achieve its maximum power. Alack of fuel or oxygen at the anodes or cathodes essentially means thatthe fuel cell is starved for chemical energy. If the anode and/orcathode are starved for chemicals, less power will be generated per unitarea (cm²). This lower power per unit area gives lower total systempower.

In a tubular fuel cell device, such as that shown in FIG. 1 where theanode lines the inside of the tube and the cathode forms the outersurface with the electrolyte therebetween, it is wishful thinking toexpect high utilization of fuel. The inside diameter of the tube, whichforms the fuel passage, is very large when compared to the thickness ofthe anode. Anode thicknesses may be on the order of 50-500 nm, whereastube diameters may be on the order of 4-20 mm. Thus, there is a highlikelihood of fuel molecules passing through the large fuel passagewithout ever entering the pores of the anode. An alternate geometry forthe tube is to have the anode on the outside of the tube. In that case,the problem could be worse because the fuel is contained within thefurnace volume, which is even larger than the volume within the tube.

Within a multilayer SOFC, such as the Fuel Cell Stick™ device 10depicted in FIG. 2 and developed by the present inventors, fuelutilization can be higher because the flow path for the gas can besmaller. FIG. 2 is identical to FIG. 1 of U.S. Pat. No. 7,838,137, thedescription of which is incorporated by reference herein. Device 10includes a fuel inlet 12 feeding a fuel passage 14 to a fuel outlet 10,and an oxidizer inlet 18 feeding an oxidizer passage 20 to an oxidizeroutlet 12. An anode 24 is adjacent the fuel passage 14 and a cathode 26is adjacent the oxidizer passage 20, with an electrolyte 28therebetween. By way of example, both the anodes 24 and fuel passages 14can be made to a thickness of 50 nm, and this similarity in thickness,where the ratio of thickness can be near 1:1 (or a bit higher or lower,such as 2:1 or 1:2) can give a more optimal chance of molecule flow intoand out of pores.

However, as the electrolyte is made thinner, such that the power per cm²(W/cm²) goes up (or as the other elements of the structure are optimizedto give higher power per area), the production of waste H₂O and CO₂within the pores will increase. So, as power per area and volumeincreases, there is an increased need to exchange the gases in theporous structure more quickly.

Therefore, there is a need to better direct the gases into the pores andto flush waste products out of the pores. Higher utilization and/orbetter flow through the pores will give better system performance.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a fuel cell devicecomprising an active structure having an anode and cathode in opposingrelation with an electrolyte therebetween, and a surrounding supportstructure including a top cover region, a bottom cover region, opposingside margin regions, and optional interposer layer regions, thesurrounding support structure being monolithic with one of the anode,cathode or electrolyte, and including a modification to its materialcomposition configured to alter the shrinkage properties of thesurrounding support structure to more closely match shrinkage propertiesof the active structure than in the absence of the modification. Themodification to the material composition of the surrounding supportstructure includes one or more of the following:

-   -   (a) where the surrounding support structure comprises a ceramic        material that is monolithic with the electrolyte, the material        composition includes an addition of anode or cathode material in        one or more of the regions;    -   (b) where the surrounding support structure comprises an anode        material that is monolithic with the anode, the material        composition includes an addition of electrolyte or cathode        material in one or more of the regions;    -   (c) where the surrounding support structure comprises a cathode        material that is monolithic with the cathode, the material        composition includes an addition of electrolyte or anode        material in one or more of the regions;    -   (d) an addition of an inorganic shrinkage control material to        the material composition that is not present in the active        structure;    -   (e) an increase in particle size used for the material        composition than the particle sizes of materials used in the        active structure;    -   (f) a decrease in particle size used for the material        composition than the particle sizes of materials used in the        active structure; or    -   (g) an addition of an organic fugitive material to the material        composition that is not present in the active structure or in an        amount greater than present in the active structure, which        organic fugitive material is removed during baking and/or        sintering of the material composition to form pores or voids in        the surrounding support structure.

In another embodiment, the present invention provides a fuel cell devicecomprising an active structure having an anode and cathode in opposingrelation with an electrolyte therebetween, an inactive surroundingsupport structure monolithic with the electrolyte and defining a firstportion of an outer surface of the device, wherein the inactivesurrounding support structure lacks the anode and cathode in opposingrelation and the active structure resides within the inactivesurrounding support structure with the anode exposed at a second portionof the outer surface and the cathode exposed at a third portion of theouter surface. The device further comprises a first surface conductor onthe second portion of the outer surface in electrical contact with theexposed anode and extending over the first portion of the outer surface,a second surface conductor on the third portion of the outer surface inelectrical contact with the exposed cathode and extending over the firstportion of the outer surface, and a non-conductive, insulating barrierlayer between the active structure and the first and second surfaceconductors extending over the first portion.

In another embodiment, the present invention provides a fuel cell systemcomprising a fuel cell device, a heat source, and an insulatingmaterial. The fuel cell device has first and second opposing ends withan elongate body therebetween comprising an active structure having ananode and cathode in opposing relation with an electrolyte therebetween,and an inactive surrounding support structure monolithic with theelectrolyte and lacking the anode and cathode in opposing relation,wherein the active structure resides within the inactive surroundingsupport structure, and wherein the inactive surrounding supportstructure adjacent the first opposing ends is larger in at least onedimension relative to a remainder of the elongate body to form a firstenlarged attachment surface at the first opposing end. At least a firstportion of the elongate body containing the active structure resideswithin the heat source for applying heat to the fuel cell device and atleast a second portion of the elongate body including the first opposingend containing the first enlarged attachment surface resides outside theheat source, and the insulating material is between the first and secondportions of the elongate body shielding the first opposing end from theheat source.

In another embodiment, the present invention provides a fuel cell devicecomprising first and second opposing ends defining an elongate bodytherebetween of length greater than width and thickness, an activestructure in the elongate body having an anode and cathode in opposingrelation with an electrolyte therebetween, and an inactive surroundingsupport structure monolithic with the electrolyte and lacking the anodeand cathode in opposing relation, the active structure residing withinthe inactive surrounding support structure, wherein the width of one orboth of the anode and cathode progressively changes along the length ofthe elongate body in the active structure.

In another embodiment, the present invention provides a fuel cell devicecomprising a multilayer active structure having electrode layers inopposing relation with an electrolyte therebetween, the electrode layersalternating in polarity from a top electrode layer to a bottom electrodelayer, and an inactive surrounding support structure monolithic with theelectrolyte and defining an outer surface of the device including a topsurface, a bottom surface and opposing side surfaces, wherein theinactive surrounding support structure lacks the electrode layers inopposing relation and the active structure resides within the inactivesurrounding support structure with at least one electrode layer of eachpolarity exposed at one of the opposing side surfaces. A first surfaceconductor resides on the outer surface in electrical contact with theexposed electrode layer of one polarity, and a second surface conductorresides on the outer surface in electrical contact with the exposedelectrode layer of the other polarity, and the first and second surfaceconductors are configured to have a designated polarity in use, whereinone or both of the first and second surface conductors extend onto thetop or bottom surface, and wherein the polarity of the top electrodelayer is the same as the designated polarity when one or both of thefirst and second surface conductors extend onto the top surface and thepolarity of the bottom electrode layer is the same as the designatedpolarity when one or both of the first and second surface conductorsextend onto the bottom surface to prevent polarity mismatches betweenthe surface conductors and the electrode layers within the inactivesurrounding support structure.

In another embodiment, the present invention provides a fuel cell devicecomprising an active structure having an anode and cathode in opposingrelation with an electrolyte therebetween, a fuel passage adjacent theanode for supplying fuel to the active structure, an air passageadjacent the cathode for supplying air to the active structure, a porousceramic layer between the anode and fuel passage and between the cathodeand air passage, the porous ceramic layer having a porosity configuredto permit transport of fuel and air from the respective fuel and airpassage to the respective anode and cathode, and an inactive surroundingsupport structure monolithic with the electrolyte and the porous ceramiclayers, wherein the inactive surrounding support structure lacks theanode and cathode in opposing relation and the active structure resideswithin the inactive surrounding support structure.

In another embodiment, the present invention provides a fuel cell systemcomprising a fuel cell device having a length between opposing first andsecond ends that is the greatest dimension whereby the device exhibitsthermal expansion along a dominant axis that is coextensive with thelength, an active heated region along a first portion of the length, aninactive cold region along a second portion of the length adjacent oneor both of the opposing first and second ends, an inactive transitionregion along a third portion of the length between the first portion andthe second portion, and an electrolyte disposed between an anode and acathode in the active heated region, wherein the anode and cathode eachhave an electrical pathway extending to an exterior surface of theinactive cold region for electrical connection. The system furthercomprises a double wall furnace comprising an inner wall and an outerwall, the inner wall defining an inner chamber therein and the outerwall defining an outer chamber, wherein the fuel cell device ispositioned with the first portion of the length within the innerchamber, the third portion of the length within the outer chamber, andthe second portion of the length outside the furnace. A first heatingelement is coupled to the inner chamber for heating the active heatedregion to a temperature above a threshold temperature for a fuel cellreaction to occur therein, and a second heating element is coupled tothe outer chamber and operable to switch between an off position wherethe inactive transition region has a temperature below the thresholdtemperature when the active heated region is above the thresholdtemperature and an on position where the inactive transition region hasa temperature above the threshold temperature for cleaning gas passageswithin the inactive transition region. A control system is coupled tothe first and second heating elements and configured to switch thesecond heating element between the off and on positions based on one ofa pre-determined cleaning schedule or a cleaning schedule triggered byreal time measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a schematic view of a tubular solid oxide fuel cell device ofthe prior art.

FIG. 2 is a schematic side cross-sectional view of a solid oxide FuelCell Stick™ device of the prior art.

FIGS. 3 and 4 are cross-sectional schematic views depicting embodimentsfor reducing shrinkage mismatch between the active structures and bulkmaterial.

FIG. 5A is a schematic end view of an embodiment for overcomingdiscrepancies between predicted and measured voltage.

FIGS. 5B-5D depict in cross-sectional end views alternative embodimentsto that of FIG. 5A.

FIGS. 6A and 6B are cross-sectional schematic end views depictinginternal non-conductive layers for insulation.

FIGS. 7A and 7B are partial perspective views depicting gas supply tubesfor feeding gas to small input holes for feeding discrete active layersor multi-layer active structures.

FIGS. 8A and 8B depict in cross-sectional end view and schematic endview, respectively, embodiments for making interconnections betweenanodes and cathodes in a multi-layer structure.

FIGS. 9A-9B, 10A-10B, 11, 12A-12E and 13 depict various embodimentshaving an enlarged end for attachment purposes.

FIG. 14 is a perspective view of an embodiment having an attachmentsurface.

FIG. 15 is a perspective view of the device of FIG. 14 connected to acircuit board using flex circuits.

FIG. 16 is a schematic top view of a device having a cross shape withfour terminating ends.

FIGS. 17A and 17B are cross-sectional views through an anode toward afuel passage depicting increasing width of the active zone down thelength of the flow path.

FIGS. 18A and 18B are schematic top and schematic side views,respectively, depicting multiple distinct gas output locations thatextend from the elongate body.

FIGS. 18C and 18D schematically depict alternative arrangements of theoutput extensions relative to the hot zone.

FIG. 19 schematically depicts a method for adding catalyst material to agas passage in a device of the present invention.

FIGS. 20A and 20B are side cross-sectional views depicting embodimentsthat address polarity mismatches between external surface conductors andinternal electrodes.

FIG. 21 schematically depicts in side cross-section a method forbuilding a device with electrodes having rounded corners.

FIG. 22 depicts in schematic perspective view a device having anelongate backbone section and distinct elongate active sectionsextending therefrom.

FIGS. 23A and 23B depict in schematic top view and end cross-sectionalview, respectively, embodiments for making series and parallel externalconnections.

FIG. 24 depicts in end cross-sectional view an embodiment having theexternal metallization penetrating inside the device for bonding to theelectrode surface.

FIG. 25 depicts in partial end cross-sectional view recessing of theexternal contact pad.

FIGS. 26A-26C schematically depict in cross-section a method forrecessing the contact pads.

FIG. 27 schematically shows in cross-section an alternative method forrecessing the contact pads.

FIGS. 28A-28D depict in schematic cross-section a method for forming aseries connection using a recessed contact pad that penetrates into thedevice to bond with the surface of the electrode.

FIG. 29 schematically depicts a method for connecting devices in series.

FIG. 30 is a partial cross-sectional view of an embodiment having porousceramic added to the top and bottom of the active structure on theelectrodes.

FIG. 31 is a schematic view of a double-walled furnace for operating andcleaning devices of the invention.

DETAILED DESCRIPTION

Reference may be made to the following publications by the sameinventors, which describe various embodiments of a multilayer Fuel CellStick™ device 10 (et al.), the contents of which are incorporated hereinby reference: U.S. Pat. Nos. 7,981,565, 7,842,429, 7,838,137, 7,883,816,8,293,415, 8,029,937, 8,227,128, and 8,278,013; and PCT Publication Nos.WO2007/056518, WO2007/134209 and WO2008/141171. The inventive structuresand/or concepts disclosed herein may be applied to one or more of theembodiments disclosed in the above-reference published applications.

In one embodiment, extra strength is given to an active layer near theedge of the area where it merges with the sides of a device 10. Activelayer (or active structure) generally means here a combination ofelectrolyte, anode and cathode. Similar thicknesses of anode and cathodemay be used, e.g., 25 or 50 μm thickness, and the electrolyte can varyfrom 10 μm to 125 μm. But these dimensions are not meant to berestrictive, and in fact, the concept of this embodiment is compatiblewith anode or cathode supported structures, in which either the cathodeor anode is much thicker than the other two layers. Also, while the useof three layers together is described, namely anode, cathode andelectrolyte, there are many other combinations in which the anode orcathode can each be made from multiple layers of compatible materials inorder to give a preferred performance—for example an anode made from twoanode layers that have varying amounts of porosity or conductivity, suchthat one layer emphasizes the property of gas transport, while the otherlayer emphasizes the property of electrical conductivity. Thus, any ofthe three “layers” that form the active layer may comprise multiplelayers. Similarly, anodes and cathodes may have many additives thatdifferentiate them from structures used in the past. In reference to asingle active layer in a device 10, with gas pathways above and below,and surrounded by the bulk structure, where the active layer approachesthe side structure or margin in a multilayer fuel cell, there can be apoint of weakness where the anode and cathode become thinner. This mightnot be desired in the overall design, but might occur due to alignmentissues. The weak spot can occur because the anode and/or the cathode endbefore the active layer touches the wall of the fuel cell, so that theedge of the active area near the wall is actually thinner than thelarger active layer itself. This thin region creates a point of weaknessthat can crack, break or tear during manufacturing or use, and therebycause a leak of gas and degrade the performance of the fuel cell.

The active layer can be designed to travel into the wall (surroundingsupport structure) of the fuel cell in order to increase the strength ofthe active layer structure. While this may have certain advantages, itmay not be enough to give the strength that is desired. Although theactive layer is not thinner in this region because the entireactive-layer structure extends into the wall, there is a point of stressconcentration in this area of transition of the active layer into thewall.

One solution then is to add thickness to the active layer through theuse of extra material. The extra material may be ceramic tape made ofzirconia, which is the same material used in the electrolyte and alsothe walls of the device. The extra material can be the same thickness asthe electrolyte, or thicker, or thinner. A key variable is the totalthickness, as compared to the total thickness of the active areastructure. In one embodiment, the anode and cathode do not stick intothe wall of the structure; in another embodiment, the anode and cathodedo stick into the wall of the structure.

To minimize stress concentration, the boundary of the added material cangradually decrease from the full thickness to zero. This can be achievedin several ways, such as through the use of multiple layers of tape orprinted material, which are staggered, or through choice of materialproperties that allow the tape to reduce gradually on its own, such asthrough the use of soft materials that deform during lamination. Similarthickness can be added in other areas of the active layers. One examplewould be in a region between cells. While the outer edges might extendinto the walls of the device, the center regions could be unsupported.The extra material that is added is conveniently made of zirconia, butthat is not the only choice allowable. Many other materials could givethe desired strength, including other ceramics and combinations ofceramics. Those materials could be fully dense or could be porous.

With reference to FIG. 3, fuel cell devices of the present inventioninclude one or more active structures 50 (or cells) in which an anode 24and a cathode 26 are in opposing relation with an electrolyte 28therebetween, and a surrounding support structure 29 that forms thewalls of the device 10. The surrounding support structure 29 may be oneof the electrode materials (e.g., an anode-supported structure), but ismore typically a ceramic material that is monolithic with theelectrolyte 28 in the active structure 50 by virtue of being co-sinteredtherewith. In an elongate structure, the surrounding support structure29 includes a top cover 52, a bottom cover 54 and side margins 56, aswell as any interposer layers 58, and constitutes the bulk of the device10. As has been previously reported, the bulk structural material(designated as ceramic 29 in FIG. 2) can be the same material or adifferent but compatible material than the material used for theelectrolyte 28. According to embodiments herein, the bulk material usedfor surrounding support structure 29 may be modified, in one or moreareas, relative to the electrolyte material to achieve one or moreadvantages as set forth below.

Shrinkage differences typically exist in the materials used to constructthe fuel cell devices 10. The fuel cell devices 10 may be constructed bylayering green tape materials and/or printing green materials over otherlayers, followed by pressing and sintering the layered structure. Theshrinkage differences between materials in the different layers canmanifest at various temperature ranges of processing, such as duringbake out in the range of several hundred degrees C., or during thesintering phase near 1300° C. to 1500° C. When several materials arematched together, as in the active structure 50 where the anode 24,electrolyte 28 and cathode 26 are combined, the shrinkage can bedifferent from the shrinkage behavior of the layers that form thesurrounding support structure 29. Although the shrinkage of eachmaterial can be modified through the choice of particle size, calciningor organic loading, still these properties may not match exactly.

In one embodiment of the invention, to better match the shrinkage of theactive structure 50 and the surrounding support structure 29, one ormore of the materials used in the active structure 50 is added into thematerial used in one or more areas of the surrounding support structure29. In one example, a NiO rich material, commonly used for anodes, isadded into the surrounding support structure material made of mostlyzirconia. NiO rich material has the advantage of being non-conductivewhen fired in an air atmosphere, such that it will not cause anelectrical problem within the device 10. Through the addition of thismaterial, the shrinkage of the bulk material layers can be modified tomore closely match the shrinkage of the layers of the active structure.The NiO rich material may include YSZ to give chemical compatibility andto promote adhesion.

The material added to the bulk layers, indicated by dashed lines in FIG.3, can be co-extensive with the entire structure, as shown in the topcover 52, or can cover only a smaller area, as shown in the interposerlayer 58, or can only match the area of the active structure 50 itself,as shown in the bottom cover 54. Although not shown, the addition alsocan be smaller in area than the active area.

In some fuel cell devices, the bulk material of the surrounding supportstructure 29 can be a majority zirconia, where the shrinkage of thatbulk material is higher than that of the layers in the active structure50. But the opposite is possible also, depending on the factorsdescribed above, like particle size, calcining and organic loading (andother factors). The relative shrinkage of portions of a fuel cell device10 can be modified, in accordance with the invention, by the addition ofactive material into the covers 52, 54 and side margins 56 of thesupport structure 29 so as to make the bulk material shrink more, orshrink less, during processing. Also, other materials could be added tocontrol shrinkage that are not one of the ingredients existing in thesupport structure 29. Alumina could be added, for example.

The surrounding support structure 29 can also be made of multiple layersof alternating materials. For example, alternating composite layers ofNiO (anode material) and LSM (cathode material), each having some YSZ(electrolyte material) added to form the composite, can be used, to bestmimic the composition of the active structure 50. Substantially morethan one or two total layers of added material may be used. In thecovers 52, 54 of fuel cell device 10, five layers each of more than onematerial could be added to give substantial matching to the activestructure 50.

In another embodiment of the invention to address shrinkage differences,the bulk material of the surrounding support structure 29 is made usinglarger or smaller particle size than the particulate size used in thelayers of the active structure 50. For example, in a device 10 where thebulk material is made from zirconia, a larger or smaller particle sizewill give alternate shrinkage behavior when compared to the standardzirconia material used for the electrolyte 28 and surrounding supportstructure 29. The same concept applies with other materials besideszirconia, including various doped zirconia formulations (e.g., differentlevels of yttria) or alternate types of electrolytes used in SOFCs. Thisconcept further applies to devices constructed in an anode-supported orcathode-supported way (in which anode or cathode style material formsthe covers 52, 54, side margins 56, and interposer layers 58).

Another embodiment for modifying the device materials is to add orremove oxides that can modify the shrinkage of the bulk material. Forexample, alumina as an addition to zirconia in small percentages (in therange of 0.05% to 0.5%, but possibly higher or lower) will allow thezirconia to sinter at a lower temperature. This modifier can be addedinto the active structure 50 but not in the bulk material, for example,to modify the shrinkage. Other additives could be used, instead ofalumina, to work in a similar way.

Another embodiment to modify the shrinkage of the surrounding supportstructure 29 is to add more organic material to the ceramic tape used asthe bulk material. For tape casting, the organic material can commonlybe made from vinyl or acrylic, but many other organic materials may besuitable. Additional organic content in the tape that is used for thebulk material can make the surrounding support structure material shrinkmore. This concept is useful even if ceramic tape is not the only methodof building up the device 10. For example, some materials are screenprinted instead of using a tape process, and addition of higher organiccontent in that format would also result in higher shrinkage.

In another embodiment, the bulk material used for the surroundingsupport structure 29 is modified to achieve additional strength in thedevice 10. Specifically, a different material is selected for thesurrounding support structure 29 than used in the active layers toimpart a higher strength to the surrounding support structure 29. Thisdescription will focus on zirconia, but is applicable to other materialsystems also by analogy.

It is known in the industry that zirconia with 8% yttria (8% YSZ) addedgives good performance as an SOFC active layer, meaning that it willtransport oxygen ions at a high rate. However it is also known thatzirconia with 3% yttria (3% YSZ) added gives good performance forstrength, such that it is often used to make structural zirconia piecesfor mechanical uses. In certain embodiments of the invention, these twomaterials are combined into one device design, such that the activestructure 50 using 8% YSZ has high ionic conductivity while thesurrounding support structure 29 using 3% YSZ has higher mechanicalstrength, giving an advantage to the overall system durability. Whilethe 3% YSZ is commonly known to have high strength, that is not to saythat the strength of the 8% YSZ is weak; it is actually quite strongalso, but it is possible that the overall system durability could beimproved using this technique.

Additional advantages can be achieved by reducing the amount of zirconiain the surrounding support structure 29. Zirconia is a relativelyexpensive material, such that cost reduction is one advantage.

In one embodiment, air gaps are introduced into the bulk material of thesurrounding support structure 29 in place of zirconia, as depicted inFIG. 4 in schematic cross-sectional view. In the manufacture of anodes24 or cathodes 26, pore-forming materials can be added thereto to creategas pathways; a similar approach of using fugitive materials can befollowed with the bulk material albeit for a different purpose.

Various organic materials can be used that will burn out cleanly from aceramic material, leaving voids. Any material that will leave an emptyspace or void after sintering is a possible choice. These organicmaterials can be varied, including polymer balls, graphite, or any otherfugitive material, but a suitable choice is polymer beads, for examplemade by Sekisui of Japan. These polymer beads or particles burn outcleanly from the ceramic during the bake and sinter profile, and theyhave the advantage that they are made using materials that will noteasily dissolve in solvents (meaning that the polymer beads cansuccessfully be processed in a solvent environment without having theparticles dissolve, which is useful for example in solvent-based tapecasting).

When these particles or beads are used in formation of pores in an anode24 or cathode 26, the goal is to have pores that are on the scale of 0.1μm to 15 μm, commonly. To reduce the amount of zirconia that is used inthe surrounding support structure 29 of a device 10, the pores formedcan be the same size or much larger, for example, on the order of about10 μm, about 50 μm, or about 250 μm. For each pore formed, an equivalentamount of zirconia is saved.

In addition to the mass savings (and therefore cost savings), anadditional advantage is reducing the thermal mass of the device 10 inthe bulk surrounding support structure 29. That reduction can allow thedevice to heat faster, and with less added heat to achieve a desiredoperating temperature. With a lower mass, a given device could furtherbe more resistant to thermal shock because it can heat or cool morequickly. Yet another advantage is the reduction of the total systemweight, which may be useful in various applications, including airborneapplications.

Rather than pores, alumina can be used as the substitute in thesurrounding support structure 29 for all or a portion of the zirconia,for the purpose of saving cost, as alumina is commonly less expensivethan zirconia. The bulk material can be made from tape that is cast fromalumina and then used in the layered assembly. Care must be taken tohave the alumina match the zirconia in the active structure 50 so thatthe materials do not come apart. One method is to add a certainpercentage of zirconia to the alumina to help match the materials. Thezirconia savings would be proportional to the amount of aluminasubstituted for zirconia. Also, a boundary layer that provides adhesionbetween a region high in zirconia and a region high in alumina may beuseful. This boundary region might be made from approximately halfzirconia-half alumina. The zirconia and alumina materials system is usedas an example, however, the principle can easily be extended to othermaterials systems that are used in SOFC devices.

As has been discussed, zirconia is a commonly used material in fuelcells. Because zirconia is an ionic conductor, a voltage can be measuredacross a bulk of this material when there is a lack of oxygen on oneside versus the other. On the one hand, this is the basic principle ofthe SOFC: fuel on one side of an SOFC layer provides the lack of oxygen,and air or O₂ on the other side provides the opposite, and together thisgives the driving force for the fuel cell. In multilayer devices of theinvention, this can provide a challenge. When conductors are placed onthe outside surface of the device, there can be a net voltage that ismeasured between the outside surface and the inside pathways in theactive structure. The result is that on a fully functioning, optimaldevice that should give an open circuit voltage (OCV) in the range of1.0V to 1.3V, a lower voltage may be measured. From a practical point ofview, it appears that this lack of optimal (as measured) OCV resultsfrom the voltage drop between the outside conductor on the device andthe internal conductor. By way of example, instead of measuring 1.1VOCV, the measurement may be near 0.85V OCV.

This presents a practical problem in development, because it isdifficult to know whether the device is performing to optimal standards.In addition, this problem could make it difficult for an automatedsystem to adequately monitor the device in operation. Because power isequal to the voltage times the current, if the voltage can't beaccurately predicted, then the power can't be accurately predicted. Inaddition, it is possible that having this kind of loss on the cell coulddegrade the performance per se, such as by reducing the driving forcefor the operation, though this can't be stated with certainty.

To overcome this discrepancy between the predicted and measured voltage,and as depicted in schematic end view in FIG. 5, a portion of thesurface of the device 10 may be coated with glass or othernon-conductive, insulating material before or after sintering to form asurface non-conductive layer 60 between the surrounding supportstructure 29 and the surface conductors or contact pads 44, at least inareas where the surface conductors 44 will be located but are not indirect contact with the anodes 24 and cathodes 26 exposed at thesurface. By non-conductive, reference is made to conducting ofelectrical voltage and current in the traditional sense and/or ionicconducting, for example, transporting of oxygen or some other atomicconstituent.

A colored glass may be used to provide a contrast that would alloweasier inspection as to the coverage over the white ceramic, though aclear glass would also be suitable. A non-conducting ceramic can also beused, for example NiO when the device is used in an air or oxidizingatmosphere (e.g., the surrounding gas is air). With the non-conductingceramics, other oxides may be added in to give special properties, suchas adhesion. For example, a small fraction of zirconia can be added toNiO for adhesion to bulk zirconia used for the surrounding supportstructure 29, or aluminum oxide (alumina) can be added for adhesion tothe surrounding support structure 29 when also used to substitute forall or a portion of the zirconia in the bulk material as discussedabove. Many other materials could be used, such that they give theproperty of providing a non-conductive barrier between the surfaceconductors 44 and the surrounding support structure 29.

Based on using different types of materials, the assembly of thissurface non-conductive layer 60 can occur before or after firing. Forexample, glass that contains a softening point below the sinteringtemperature of the ceramic is best placed on the structure after thesintering process due to the high mobility of the glass above thesoftening point. By way of example and not limitation, after a sinternear 1300-1400° C., the glass can be added by screen printing onto thesurface and then firing at a temperature near 800° C.

In FIG. 5A, a multilayer active structure 50 is shown with the anodes 24exposed to the left side margin 56 and the cathodes 26 alternatinglyexposed to the right side margin 56 of the device 10. The contact pads44 are applied to the top cover 52 and the respective side margin 56 tomake contact with the exposed anodes 24 or cathodes 26. The surfacenon-conductive layer 60 is applied to the surface of the top cover 52 ofthe surrounding support structure 29 before applying the contact pads 44to provide a barrier therebetween. The surface non-conductive layer 60is not applied on the side margins 56 to avoid areas where the contactpads 44 must make electrical contact with the exposed anodes 24 andcathodes 26, and is not applied to the bottom cover 54 where the contactpads 44 are not applied, as no barrier is needed there.

In FIGS. 5B-5D, variations on possible coating configurations similar tothat of FIG. 5A are shown by way of example but not limitation. In thepartial cross-sectional end view of FIG. 5B, the top cover 52 does notextend completely to the side of the device 10 so as to expose a smallsurface of the anode 24 at the top of the device 10. The same can bedone for the cathode 26 at the bottom of the device 10, though notshown. The surface non-conductive layer 60 is then applied to the topand bottom covers 52, 54 and the contact pads 44 are applied over thenon-conductive surface layers 60 and extend to the side to cover theexposed anode 24 (and cathode 26). The side margins 56 are leftun-coated. This embodiment lends itself to a tape casting method forforming the entire device 10. In FIG. 5C, which is similar to FIG. 5Bwith respect to the anode 24 being exposed at the top surface, thecontact pad 44 is applied to the side margin 56 and extending slightlyonto the top and bottom thereby covering the exposed anode 24 (andcathode 26), such as by dipping the sides into a plating bath until thepoint where the top cover 52 begins, or by screen-printing. The surfacenon-conductive layer 60 is first applied to the side margins 56 forapplying the contact pads 44, and can also be applied to the bottomcover 54. In FIG. 5D, the surface non-conductive layer 60 is applied tothe entire surface except where the anode and cathode are exposed at theside margin, which can easily be done with tape casting, and then theside margins 56 of the device 10 can be dipped in the plating bath orscreen printed to apply the contact pads 44.

In an alternate example, NiO can be added to the surfaces of thesurrounding support structure 29 before sintering of the entire device10. This NiO can be made into a tape form, and then laminated onto thesurface in order to give a simple process that provides a uniformly thinsurface non-conductive layer 60. Alternate methods can be used to adherethe NiO onto the green device, such as screen printing. There arevarious ways to provide a surface non-conductive layer 60, includingadding it before or after the sintering step, as can be appreciated bypersons skilled in the art. Similarly, the contact pads 44 can beco-fired conductors, as well as added to the surface after firing. Interms of co-fired conductors, precious metals, such as platinum, can beused or conductive oxides, such as LSM. A wide variety of materials arecompatible as conductors, and the surface non-conductive layer 60material may be selected based on the materials used for the surroundingsupport structure 29 and the contact pads 44.

According to another embodiment, another way to achieve the insulatinggoal is to build the non-conductive layer inside the device at the timeof manufacturing. This is similar to the NiO coating described above,but it can be put inside the surrounding support structure 29 as aninternal non-conductive layer 62, as shown in FIG. 6A, to effectivelybreak up the continuity of the bulk material between the activestructure 50 and the surface(s) on which the contact pads 44 reside. NiOis just an example, as many other materials can meet the need in asimilar way, of being non-conductive to electrons, or to ions, or bothat the same time. By putting the non-conductive layer 62 into thedevice, instead of using it at the surface, some advantages can beobtained. The issue of adhesion of the material to the surface can berelieved, since the oxide layer is covered on both sides by the bulkmaterial of the surrounding support structure 29 instead of on just oneside. Also, the outside appearance of the device 10 can be maintained ina uniform style, such as the all-white look of the zirconia body.Further, an oxide layer can be more easily automated into themanufacturing process by making it part of the internal design. Finally,the advantage of putting the non-conductive layer 62 into the structure29 is that the material can be placed in any location within the device10, and can reduce the amount, and thus cost, of the bulk material asdescribed above. By way of further example, the dashed lines in FIG. 3could represent internal non-conductive layers.

Where the electrode (anode 24 or cathode 26) or an internal conductor isbrought out to the edge of the device, i.e., the conductor extends fromthe internal anode 24 or cathode 26 out to a contact pad 44, it may beuseful to have passivation under the electrode or internal conductor inthe inactive region where it is exposed to air (or fuel, whatever theatmosphere is outside the device). However, when this electrode is builtas part of the initial green construction of the device, it is notpossible to add passivation under the fired electrode (unlike the otherregions on the outside of the device, where the non-conductive layer canbe coated first, followed by adding the conductors.) Thus, FIG. 6B showsan internal non-conductive layer 62 built into the device under theelectrode (shown with anode 24) in the side margin 56 of the surroundingsupport structure 29 to separate the conductor from the bulk material ofthe stick (for example, the YSZ).

It is noted that nickel oxide is used in two different chemical statesin the structure overall. When NiO is used in the anode, there is areducing gas present and some large portion of the NiO reduces to Nimetal, thereby providing an electrically conductive material. On theother hand, when NiO is used as an electrical insulator in the zirconiamaterial, or on the surface of it, there is no reducing atmosphere (orat least not a substantially reducing atmosphere to change the state ofthe Ni) and therefore the NiO will remain as a non-conductive oxide.

The publications referenced above disclose the use of relatively largetubes placed over the ends of the device that can access the entrypoints of the gas passages 14, 20, which have typically been depicted asrelatively large openings, formed by burn-out of sacrificial layers orremoval of wires after lamination. An alternative is to put multiplesmall openings at the end of the device for gas to enter, which openingsare then fluidicly coupled to the larger gas passages 14, 20. In thisdesign, the large tube would then allow gas to pass into all of thesmall holes that have been created. For example, latex tubes or metaltubes can be used, and these tubes can be sealed with glue, adhesive orepoxy.

In an alternative embodiment, depicted in FIGS. 7A-7B, small input holes70 can be used to supply gas individually to discrete active layers ormulti-layer active structures within the device 10 using multiple gassupply tubes 72. One advantage is that during testing, it is importantto check for leaks within the device 10. If gas is inputted into justone hole that is coupled to just one of multiple active layers or tojust one of multiple multi-layer active structures, it can then bedetermined if the gas exits from just one other hole. During use, thedevice 10 could be operated with less than the available active layersor structures, if desired, by flowing gas into less than all of theinput holes 70.

In one example, the input holes 70 are created by wires (not shown) thatare approximately 0.040 inch. The wires are removed in the green state.After sintering, the input hole diameter is a uniform 0.032 inch. Fortesting, a small metal tube, often made from stainless steel, with anoutside diameter of 0.030 inch can be used. These tubes are commonlyavailable for dispensing applications, with varied lengths anddiameters, and may conveniently include an adapter that easily mateswith a gas supply line. A tube is inserted into one of the input holes70 on the device 10, and a sealant is applied. The sealant can be madefrom a variety of materials: organic adhesive such as latex rubbercement or glue; inorganic adhesive such as silicone; or high temperaturesealant such as a glass type material.

This method can be used for operating a device 10 having at least onecold end 11 a that extends outside of a furnace 76, as shown in FIG. 7A,whereby the gas supply tubes 72 are sealed into the input holes 70outside of the furnace. Alternatively, this method can be used with adevice 10′ that does not extend from the furnace 76, as shown in FIG.7B, where a multitude of tubes 72 can make connection to a hotmultilayer fuel cell structure inside the furnace 76, and only the gassupply tubes 72 would exit from the furnace 76. In this example, thesealant at the ends of the gas supply tubes 76 would be the hightemperature type, such as a type of glass. The dashed lines representthe boundaries of the heated area, such as a furnace wall. Additionally,in these embodiments, the tubes can also be made out of ceramic, whichmay be co-sintered with the surrounding support structure 29.Alternatively, if the gas supply tubes 72 are made out of metal, theycan at once carry gas and carry electrical current and or voltage.

FIG. 8A depicts one embodiment for making an interconnection between theanode 24 and cathode 26 in a multilayer structure. In relatedapplications referenced above, several methods of interconnecting ananode and cathode have been shown, including one where the interconnectmaterial would extend through the bulk material of the device, mostcommonly YSZ, into both the anode and cathode. Many variations arepossible on this structure, for example the conductive material can bemade out of a precious metal (Pt, Pd, Ag, Au, or alloys and combinationsthat contain one or more of these metals), or out of a non-preciousmetal alternative such as LSM or other conductive ceramic, or stainlesssteel or other non-oxidizing metals. However precious metal is presentlybelieved to be superior in terms of conductivity. More importantly, thematerial used for an interconnect conductor must be resistant toreduction (giving up its oxygen) on one side, and/or oxidation on theother side. It is anticipated that such materials that have goodstability in oxidizing and reducing atmospheres and high conductivitywill be created over time. Further, the interconnect conductor can be amixture of conductive and non-conductive materials, such as a blend ofprecious metal and YSZ that would give both conductivity and adhesion tothe bulk ceramic (YSZ). Or, the precious metal can be coated aroundceramic particles, as a way of reducing the quantity of metal used.

One of the key challenges for the use of precious metal as aninterconnect conductor is to reduce the amount of metal as much aspossible, in order to lower cost. In one embodiment, shown incross-section in FIG. 8A, an alternative solution is to have the anode24 and cathode 26 overlap, and to provide a thin interconnect conductor80 between them. In this design, the interconnect conductor 80 would benon-porous in order to keep the oxidizing and reducing atmospheresseparate. As above, precious metals or non-precious conductors can beused, with precious metals being advantageous in many ways, except fortheir cost. Other alloys or conductive ceramics would work also, iftheir material properties can handle the reality of the workingconditions, or the interconnect conductor 80 can be a mix of materials,precious metals coated onto a non-conductive core to save on quantityand therefore cost, and/or can have portions of ceramics added in tohelp with adhesion to the anode 24 and/or cathode 26. In any event, theinterconnect conductor 80 should be continuous and non-porous in orderto keep the oxidizing and reducing atmospheres separate.

It should also be seen that these anode and cathode areas overlappingwith the intervening interconnect conductor 80 are not necessarilyanodes 24 and cathodes 26 that are functioning as an active layer, inthis region near the interconnection. The anode and cathode materials,in one embodiment, are extensions of the anode and cathode material awayfrom the active structure 50 toward an area that is devoted to thisinterconnect. One advantage is that the amount of air and fuel is notsubstantial (that is, while the amount of air and fuel is enough tomaintain the oxidative or reduced state of the cathode 26 and anode 24in the active area, the gases are not flowing in large quantities in theinterconnect area. This is useful because, while the desire of theinterconnect conductor 80 is to act as a barrier seal between anode 24and cathode 26, such a material is unlikely to be completely non-porous.Small holes may exist. It is expected, however, that equilibrium can beachieved to allow the materials to stay in their proper oxidized/reducedstates.

FIG. 8B schematically depicts how this overlapping area may interactwith the larger device design. In this case, the overlapping anode 24,cathode 26 and intervening interconnect conductor 80 act to connect twocells or active structures 50 in series (i.e., connects the cathode 26of one cell to the anode 24 of the next cell). It is further possibleand advantageous to have various material variations in the anode orcathode construction. Properties like ionic conductivity, electricalconductivity, and porosity can all be optimized for certain regions ofan anode or cathode. For example, though depicted as a homogeneousmaterial, the portion extending into the interconnection area may have avariable composition from that portion of the anode 24 or cathode 26 inthe active structure 50.

As may be appreciated, the various designs for the fuel cell devicesdiscussed herein and in the related applications can be made relativelylarge or small. At the large end, it may be envisioned that they can beused to power large transport ships. At the small end, they can be usedto power miniature devices such as small electronics, for example phonesand other electronic gadgets. To better enable use as miniature fuelcell devices, certain improvements or modifications may be made, asdiscussed more fully herein below.

FIG. 9A shows a device 10 that is similar to previously describeddevices 10, having an elongate body between opposing ends 11 a, 11 b,but with several modifications. One end 11 a may be made larger than theelongate body of the device 10, which can be useful if the scale of theelongate body does not allow convenient attachment to a desiredsubstrate. For example, if the elongate body has a thickness z of 0.5mm, then it would be useful to have a thickness Z at the end 11 a of 2-4mm to allow for easy attachment and/or to allow for higher strength atthe attachment point. The attachment surface 88 of end 11 a is furthershown with an adhesive or attachment material 90 thereon to facilitateattachment to a substrate 92, as shown in FIG. 9B. The input holes 70provide entry points for the gas to enter the device 10 through thesubstrate, as desired.

The elongate body in which the active structure(s) 50 reside (asrepresented by the circuit symbol) is shown as being thinner than theend 11 a of the device 10, but it also could be narrower in width y thanthe width Y of the end 11 a, as shown in FIG. 9B. For example, theactive structure 50 of the device 10 should not be any larger thannecessary in order to allow rapid heating and reduced chance of thermalshock. The device 10 can stand up tall on the larger end 11 a, and theattachment material 90 can hold it in place. The input holes 70 can besurrounded by the attachment material 90, so that the attachmentmaterial 90 provides the mechanical attachment but also provides asealing mechanism around the gas entry points. As further shown in FIG.9A, the large end 11 a of the device may be a cold end positionedoutside a heat source 76, such as a furnace or hot box, and shieldedfrom the heat source 76 by insulating material, such as a furnace wall,and a portion of the elongate body having the smaller dimensions andcontaining the active structure(s) 50 may be contained inside thefurnace 76 to form an active reaction zone for the fuel cell.

FIGS. 10A-10B further show use of gas supply tubes 72 as the attachmentmechanism for the device 10 in addition to supplying the flow of gasinto the device 10, as shown by the arrows. The gas supply tubes 72 areinserted into the end 11 a of the device 10, and can be made from manymaterials, organic or inorganic, metallic or ceramic, that havesufficient structural integrity to support the device 10. If the gassupply tubes 72 are also conductive, they can serve the additionalpurpose of conducting electricity to the active structure. Attachmentmaterial 90, such as solder, adhesive, or glue, can seal the tubes 72into place. The attachment material 90 can extend into the device 10, sothat it attaches the tubes 72 to the inside walls of the device 10. Asfurther depicted in FIG. 10A, the small device 10 can have resistanceheating elements 94 on the surface of the device 10 to provide heatingduring start up and operation. The resistance heating elements 94 canhave a serpentine pattern for even heating, or can be straight. Endcontacts 96 for the resistance heating elements 94 can come out to thecold end 11 a of the multilayer device 10, for easy connection. Thedevice 10 may be placed with the elongate body extending into a furnaceor other heat source 76 similar to shown in FIG. 9A. The end contacts 96can be attached using solder to a circuit board, as shown and discussedhereafter.

FIG. 11 shows the device 10 having the attachment surface 88 of a largecold end 11 a mounted to a substrate 92, such as a circuit board, andthe smaller elongate body with the hot reaction zone and hot end 11 bcontained inside insulation 98. The insulation 98 can be made fromceramic fiber insulation, mostly containing alumina-silicate ceramic, orany other suitable type of insulation. The substrate 92 may beconfigured to provide the flow of gas into the device 10, as depicted bythe arrows.

For surface mounting, device 10 can be shaped similar to an arch, withattachment surfaces 88 at both enlarged ends 11 a, 11 b, as depictedschematically in FIG. 12A. Each of ends 11 a, 11 b are cold ends formounting to a substrate outside and/or shielded from a furnace or otherheat source 76, and only the portion of the elongate substratetherebetween containing the active structure 50 is exposed to the heatsource 76. The two point attachment can give good mechanical stabilityin case of vibration, and flexibility of the substrate can preventcracking in the device 10. The attachment material 90 can be conductiveor non-conductive material. Solder is an example of a conductivematerial. The attachment material 90 can provide both the electricalattachment into the fuel cell and the gas-sealing attachment, asdiscussed above. End 11 a is enlarged to show the attachment surface 88in better detail, including attachment material 90 and input hole 70. Inan alternative embodiment, depicted schematically in FIG. 12B, theelongate body and a portion of the large ends 11 a, 11 b reside in thefurnace or heat source 76, with only the portion containing theattachment surfaces 88 of the large ends 11 a, 11 b extending outsidethe furnace 76 for attachment to a substrate. FIGS. 12C-12Eschematically depict further alternative embodiments of devices 10 withboth ends 11 a, 11 b having attachment surfaces 88. FIG. 12C is a curvedarch instead of being square at the corners. The curved arch shape iseasily achieved in a multilayer ceramic device 10, either throughmachining or through special lamination onto a shaped surface, or bysome other method. The curved arch shape can reduce mechanical stress ina device 10 that is subject to heating and cooling. FIGS. 12D and 12Eare similar devices 10 and differ from the device 10 of FIG. 12A byextending the elongate body vertically from the ends 11 a, 11 b, withFIG. 12D depicting a lower vertical profile and FIG. 12E depicting ahigher vertical profile.

As schematically depicted in FIG. 13, the device 10 can have amechanical notch 100 in the attachment surface 88 to keep portions ofthe attachment surface separate from each other (such as to preventsolder wicking between pads). In addition, the thinning and/or narrowingfrom the enlarged end 11 a to the elongate body can be curved, to avoidsharp edges, as shown.

As further shown in FIG. 13, the device 10 can have input holes 70 inthe enlarged end 11 a for attachment of gas supply tubes 72 for gasentry into the fuel cell in addition to and separate from an attachmentsurface 88 for mechanical attachment to a substrate. In addition, one orboth of the attachment material and gas supply tubes 72 can beconductive to provide electrical connection into the fuel cell. Further,more than one area of attachment material 90 can be used, for examplethe device can have two or four areas of attachment material 90, whichcan be useful for serving two or more distinct internal fuel cellregions. Thus, multiple conductive areas of attachment material and/oruse of conductive gas supply tubes can provide additional electricalattachment points to the device 10.

FIGS. 9A-13 have focused on one or both ends 11 a, 11 b being enlargedfor attachment purposes relative to the main portion of the elongatesubstrate, which contains the active structure(s) 50 for the activereaction zone. However, certain features described in those embodimentsmay also be useful for the elongate substrate design having uniformlength, width and height from one end 11 a to the other end 11 b. FIG.14 depicts a device 10 of uniform dimension that is easier tomanufacture because of that uniformity, but that also includes anattachment surface on only one end 11 a of device 10. The attachmentsurface 88 that mounts to a substrate includes the input holes 70 forgas entry and the electrical connections by virtue of using conductiveattachment material 90. The opposite end 11 b and the portion of theelongate substrate adjacent thereto and containing the activestructure(s) 50 are exposed to and/or extend within a heat source 76.

In one embodiment, shown schematically in FIG. 15, gas supply to theinput holes 70 can be achieved with flex circuits 110. Flex circuits areused in modern microelectronics and are distinguished by theirflexibility. They are most commonly made from polyimide tape, such asKapton® by DuPont, which has good temperature stability. Because thismaterial is easily formed into shapes and/or may be multi-layer, theflex circuits 110 can be made to contain an open pathway 112 within theflex circuit 110. This pathway 112 can carry gas to the miniature fuelcell device 10, and can also carry the electrical connections 114 to andfrom the conductive attachment material 90. The flex circuits 110 couldattach to the device 10 of FIG. 14, for example. The feed of gas to theflex circuits 110 could come from another set of soldered or gluedconnections. The flex circuit 110 is unique in the present inventionbecause of its dual role as electrical circuit and gas flow provider.

In addition, the flex circuit could contain all of the necessary controland processing circuitry to serve the fuel cell device 10. A connectorcould connect to the other circuits in the device 10, and anotherconnector could attach to a thermocouple for additional control of thefuel cell device 10. Gas supply could be attached to the flex circuits110 using glue or solder, or could be done through a temporaryattachment means where the flex circuit mating area is clamped intoplace on the gas supply. One advantage of this flex circuit method isthat the fuel cell device 10 is free of rigid connections, and istherefore more resistant to cracking or physical damage.

In an alternative embodiment, a device 10′ is depicted in schematic viewin FIG. 16. Device 10′ has an elongate substrate extending between firstand second opposing ends 11 a, 11 b and contain active structure(s) 50therebetween and entirely within the internal support structure. Theelongate substrate has a length that is the greatest dimension such thatthermal expansion is dominant in that length direction. The elongatebody, including ends 11 a, 11 b, is however contained within a heatsource 76, such as a furnace. The device 10′ further includes projectingportions that extend outwardly in the width direction from the elongatebody and out of the heat source 76, terminating in cold ends 11 a′, 11b′. The length between cold ends 11 a′, 11 b′ is less than the lengthbetween hot ends 11 a, 11 b, but still greater than the width andthickness of the section between ends 11 a′ and 11 b′. Thus, the device10′ has a cross shape with four terminating ends, with the largest areaand dimensions of the device 10 inside the hot zone where theyexperience temperature stability, and two smaller terminating ends thatexperience temperature gradients along the length direction that exitsfrom the heat source 76. By this design, gases are fed into the device10 from cold connections to ends 11 a′, 11 b′ outside the heat source 76and electrical connections can likewise be made outside the heat source76, while the majority of the device 10′ including the activestructure(s) 50 resides within the heat source 76 and excess gases exitthe device 10′ in the hot region.

In related U.S. application Ser. No. 12/607,384, FIG. 163 and relateddiscussion relates to an efficiency improvement in which the shape ofthe gas passage 14, 20 changes along the length of the active zone 33 bto provide decreasing volume and thus increasing flow rate in the gaspassage 14, 20 to account for the progressive differences in gascomposition as the gas proceeds down the length of the active zone 33 b.For example, as the oxygen is used up from air, more air flow volumewould be required in the oxidizer passage 20 to provide a similarcontent of oxygen to a given active zone 33 b (also true for depletionof fuel in the fuel passage 14 and its replacement by CO₂ and H₂O).Thus, in that FIG. 163, the width of the flow path narrows in order togive a higher rate of flow.

In an embodiment of the present invention, depicted in FIG. 17A incross-sectional view through the anode 24 in a direction toward the fuelpassage 14, energy efficiency may be improved in the device 10 byinstead enlarging the area of the anode 24 (and/or cathode 26) down thelength of the active zone 33 b, e.g., increasing the width of the activezone 33 b down the length of the flow path. As the gas flow rate becomesmeasurably slower the dwell time gradually increases due to theincreasing area of the anode 24 (and/or cathode 26), and this increaseddwell time will allow greater utilization of the fuel (and oxygen)molecules.

In the embodiment depicted in FIG. 17B, a similar concept is shown formultiple active structures 50 connected in series, where each activefuel cell down the length of the series combination is made slightlylarger than the preceding cell. In this way, the active cells along theflow path may then be provided with the same amount of power since theprogressively larger cells will have longer dwell time with theprogressively depleting gas composition. In other words, as the air andfuel flow down a passage, the useful ingredients in those gases aredepleted. It is natural that each cell down the length would give lowerpower than the previous cell, for example, lower voltage and/or lowercurrent, but by making each cell larger than the last, the issue iscounteracted to provide better uniformity of power output between thecells. Together, FIGS. 17A and 17B recognize that the areas of theactive structure are progressively non-uniform in size, when compared tothe direction of the flow of the gas, either becoming larger or smaller,in order to give preferred properties regarding fuel utilization ortotal power. The dimension of the active structures can increase, ordecrease, as the concentration of useful gases changes in a device, toadapt to the changing properties of the gas.

In one embodiment, a device 10 of the invention includes multiple airand/or fuel output locations. Multiple outputs may provide increasedknowledge during testing and development, for example if it is desiredto measure the power of an individual active layer and also the gas flowrates for that same layer. Multiple outputs may also be useful where thegases are to be sent in distinct directions at after they have flowedthrough the device 10.

In FIGS. 18A-18B, the device 10 is shown in schematic top view andschematic side view, respectively, having one large gas entry at eachend 11 a, 11 b of the device 10, and three output locations for thatsame gas flow direction. As shown in FIG. 18B, the device 10 may includethree distinct active layers, for example, with each fuel passage 14having a distinct fuel outlet 16 a, 16 b, 16 c and each oxidizer passage20 having a distinct oxidizer outlet 22 a, 22 b, 22 c. Alternatively,each output could be serving multiple layers.

As depicted in FIG. 18A, the hot zone could be in the center of thedevice, with the ends 11 a, 11 b of the device and the entire outputextensions with outlets 16 a-c, 22 a-c in the cold zone 30. Thisarrangement would allow for the gases to cool before leaving the device10, and thus allow for low temperature connections to be made to collectthe exhaust gases. In FIG. 18C, the hot zone 32 could be arranged suchthat the output extensions are partially within the hot zone 32, butemerging separately such that the exhaust gases are still collectedoutside the furnace, but the gases may not have cooled appreciably. Inyet another alternative, depicted in FIG. 18D, the outputs 16 a-c, 22a-c may be completely contained within the hot zone 32.

In U.S. Application Publication No. 2011/0117471, it was disclosed thata conductor metal can be added to sacrificial fibers used to form theair and fuel passages, and after removal of the sacrificial fiber, theconductive metal remains in the passages sintered to the electrodematerial providing a higher conductive path for electrons to flow out ofthe device. A similar concept of placing material in the passagesincludes the use of a catalyst for purposes of reforming the fuel.Reforming means to break down longer carbon chains into smaller carbonchains, and is often accomplished by adding heat and steam. One problemin reforming can be the deposition of carbon, e.g., in the form of ash,onto the walls of the furnace. Catalysts can help prevent this carbonaccumulation, and can promote the reforming reaction. Many catalysts areknown, including nickel, platinum, palladium, and rhodium, and thecatalysts may also be alloys or even catalytic materials on top of othersupport materials.

One method of adding a catalyst material to a gas passage, e.g., a fuelpassage 14, includes adding particles of catalyst 46 to the outside of awire 42 that is used to form a gas passage for feeding an activestructure 50, as shown schematically in FIG. 19. The particles can bepainted on, using a binder to aid in attachment, for example. The wireis then built into the device 10, as discussed in prior relatedapplications, and then the structure is laminated. When the wire 42 isremoved, the catalyst 46 is left in place within the formed passage 14.After sintering of the device 10, an integrated catalytic region exists.

Similarly, catalyst can be provided in a gap formed by fugitive orsacrificial materials, as shown in FIGS. 12, 13A and 13B of U.S.Application Publication No. 2011/0117471, which is incorporated hereinby reference in its entirety. The gap tape or fibers 41 can be formedwith a region containing particles of catalyst, and then after sinterthe catalyst will be left in place.

The location of the catalyst 46 can be chosen to be optimal whencompared to the temperature gradients that are present across theoperating device. For example, one desirable location for the catalyst46 may be in the hot zone 32 of the device 10. Alternatively, thecatalyst may be incorporated in the transition zone 31 where thetemperature is changing from cold to hot; for example, the catalystparticles could be incorporated along a region that extends from aregion that is substantially cool to a region that is substantially hot,which may include the portion of the device that passes through the wallof the furnace 76. The presence of the catalyst may help preventbuild-up of carbon materials in that transition zone 31.

In another embodiment of the invention, a device is provided thataddresses polarity mismatches between external surface conductors andthe internal electrodes. As discussed above, and with reference to FIG.5A, a voltage drop may occur between the outside conductor 44 on thedevice 10 and the internal conductor or electrode 24, which makes itappear that the device 10 lacks an optimal (as measured) OCV. Thenon-conductive surface layer 60 in the above embodiment is one methodfor addressing the issue. Another method for addressing the issue takesinto account the atmosphere in which the device operates. For a fuelcell device that is operating in an air or oxidizing atmosphere, thepolarity that exists between the outside of the device and some internallocation would be a polarity between the outside air surface and aninside fuel surface. Similarly, if the device is operating in a reducingatmosphere (for example to facilitate the use of pure nickel or copperconductors on the outside of the device), then the polarity that existswould be from the outside-fuel surface and an inside-air surface.

To reduce the interaction between the surface conductor 44 and theopposite internal electrode, the device 10 can be arranged to provideshielding between those two points. In FIG. 20A depicted in sidecross-sectional view, for an air atmosphere in furnace 76, the device 10is arranged so that the active structure 50 begins and ends with acathode 26 (e.g., air side of the cell) and also so that the gaspassages begin and end with oxidizer passages 20. The polarity betweenthe outside of the device 10, which is exposed to air, and the closestinternal passage 20, which also carries air and is adjacent the cathode26, is minimized through this construction technique. As seen in FIG.20, the surface conductors 44 can be on the ceramic surrounding supportstructure 29, or surface non-conductive layers 60, e.g., passivationlayers, can be used therebetween as described in reference to FIG. 5A,for example. In addition, the active structure 50 could be reversedwhere the atmosphere in the furnace 76 contains some amount of fuel suchthat the atmosphere is reducing, e.g., the active structure 50 wouldhave fuel passages 14 and anodes 24 closest to the surface conductors44. In general, this design allows for surface conductors 44 to beplaced on both the top and bottom surface of the device 10 because theinternal active structure 50 is coordinated with the surface, in termsof polarity.

Alternatively, the active structure 50 could be arranged to begin withair and end with fuel, but then surface conductors 44 are only placed onthe surface that has the sympathetic polarity (e.g., in a device thatexists in an air atmosphere furnace, surface conductors would only beplaced on the surface that is closest to the air passages 20). Inanother alternative, depicted in side cross-sectional view in FIG. 20B,the internal design is similar to that of FIG. 20A, but air enters fromone end 11 a of device 10, and fuel enters from the other end 11 b, butall excess or exhaust gases exit from the center of the device 10. Inthis case, the surface conductors 44 may be placed over any sympatheticportion of the device 10, which includes the top and bottom surfaces inthe example shown. While other factors in a device 10 may still lead tosome amount of misleading voltage drop in the measurement, the aboveembodiments can help reduce the issue.

The shrinkage of the layers of the active structure 50 and the effortsto have the anode 24, electrolyte 28 and cathode 26 sinter together arechallenging. Various efforts to match the materials to each other havebeen described, but challenges can still be present. One way toalleviate these problems is to round the corners of the anodes 24 andcathodes 26 when building up the green stack in order to reduce thestress concentration at any one point. FIG. 21 depicts schematically thebuild-up of an active structure 50 with layers that have roundedcorners. Other shapes are possible such that they minimize stress atcorners by eliminating sharp points or 90 degree angles. In addition,the materials of the anode 24 and cathode 26, and associated currentcollectors 84, 86, can be distributed so that they do not line up overone another in an exact pattern, as further depicted in FIG. 21. Forexample, an anode 24 can be larger than its corresponding currentcollector 84 (these are two parts electrodes, one part optimized forchemical activity, and the other part optimized for current carrying).The benefit is found because this difference spreads out the forcesassociated with the materials, through any mismatch that occurs. Thesedifferences diffuse the stress over a larger area, compared to a perfectregistration of one pattern on top of another. A similar effect can befound by providing a misalignment of an anode 24 over a cathode 26, asis also shown in FIG. 21.

To reduce the stress and expansion problems during start up, a device200 is shown in FIG. 22 that is similar in design to FIGS. 120 and 131Aof co-pending U.S. Application Publication No. 2010/0104910, which isincorporated herein by reference in its entirety. The device 200 of FIG.22 includes an elongate backbone section 202 having opposing input ends11 a, 11 b in a cold, inactive zone 30 for the fuel inlets 12 andoxidizer inlets 18, respectively. In the hot, active zone 32, aplurality of elongate active sections 204 a, b, c, etc. (collectivelylabeled 204) extend from one side 11 c (or from both sides 11 c, 11 d,not shown) and terminate at ends 206 in exhaust fuel and oxidizeroutlets 16, 22. An advantage of this design over a different design withthe same total area but in one solid piece is that this design couldhave an easier time adapting to a rapid heat-up. By breaking up thedesign into smaller elongate active sections 204, the rate of rise couldbe faster than the rate of rise on a device 10 of similar mass but onelarge area.

Each elongate active section 204 may contain one or more active cells.Cells from one elongate active section 204 may be connected in series orparallel combinations with the cells in other elongate active sections204. The elongate backbone section 202 may contain additional activestructure, or may contain only gas distribution passages, such as arteryflow paths, described in the immediately above-referenced publication.Rather than the square or rectangular shape depicted for elongate activesection 204 b, the ends 206 of the elongate active sections 204 can betapered in a scalloped fashion, as shown with elongate active section204 a, or in a pointed fashion, as shown with elongate active section204 c to reduce the dimension in the area where the excess fuel isemitted so as to reduce the expansion at the tips from the heating bythe unburned fuel. Although more complex in design, the gas passages canbe made to flow back into the elongate backbone section 202 for exitelsewhere from the device 200. For example, both gases may be inputtedat end 11 a, snake through each elongate active section 204, and exitfrom end 11 b.

As discussed in related applications referenced above, embodiments myinclude contact pads or surface conductors 44 that are applied along thesides of a device 10 to make electrical connections or contacts betweendifferent electrodes, e.g., parallel and series connections. Thefollowing includes additional embodiments for making externalconnections.

In FIGS. 23A and 23B, an anode 24 or cathode 26 from each of two activestructures 50 can be extended to the side (edge) of the device 10 and acommon contact pad 44 applied over them to form a series or parallelconnection between them (series connection shown). In FIG. 23A, a topview is depicted of a device 10 having three active structures 50 inseries down the length of the device 10. In FIG. 23B, a cross-sectionalview is depicted of two active structures 50 stacked vertically in adevice 10 and connected in series. Active structures 50 arranged in bothvertical stacks and length-wise fashion can be combined and connected inparallel and/or series arrangements to increase the power of the device10.

In one embodiment, shown in FIGS. 23B and 24, gap-forming material (notshown) is used at the edge of the electrodes when building up the greenstructure to create a larger void at the edge of the device 10 afterlamination and sintering, so that the applied metal of contact pad 44will flow into the edge of the device 10. This penetrating metal 44 athat enters the gap will form a 3-dimensional bond onto the electrode,which will give lower ESR. In FIG. 24, for comparison purposes, theanode 24 is shown where no gap-forming material was used, such that thecontact is only made to the edge or side of the anode 24, whereas thecathode 26 is shown with penetrating metal 44 a that that fills a gapand bonds to the surface of the cathode 26. Without this penetratingmetal 44 a, the anode 24 forms a point contact at the edge of the device10, which will likely have higher resistance. Having the lowestresistance possible is advantageous because these contacts may becarrying moderate or high currents during normal operation, and theycould fail (burn open) if the resistance is high. In addition, anyresistive losses at the contact pads 44 are wasted power that can't beused by the overall system. Thus, it is advantageous to have theelectrodes come to the edge of a device 10, but with a gap formed at theedge, so that the applied metal for contact pad 44 can touch the surfaceof the electrode, and not just the side of the electrode.

In another embodiment, of particular use where a side of the device 10will include multiple distinct contact pads 44, the contact pads 44 arerecessed into the edge of the device 10. In other words, the pairs ofelectrodes (one electrode from each of two adjacent cells) that reachthe edge are inside a large void 45 and the contact pad 44 is appliedwithin the void 45, as shown in schematic cross-section in FIG. 25. Anadvantage of this embodiment is the ability to form distinct edgeconnections, close to each other but not shorting. This can then berepeated many times on one side of the device 10, and the electrodeswould never be shorting. The scale of this structure, along with therepetition, could be made very small.

FIGS. 26A-26C schematically depict one method for creating recessedcontact pads 44. In FIG. 26A, voids 45 are created at the side of thedevice 10. In FIG. 26B, the voids 45 are over-filled so as to coat theside of the device 10 with metal. In FIG. 26C, the side of the device 10is sanded or ground to remove the excess material. A sintering step mayoccur between the over-filling and sanding steps, but is not necessary.Also, it is not necessary to have the excess metal, i.e., it can be afilling step rather than an over-filling step, but it is more convenientto over-fill and then clean up the side edge after firing. Further,because the metal has penetrated into gaps at the edge of the device 10,followed by a polishing or clean-up step, the device 10 is left withvery distinct metallization lines along the edge of the device 10. Inthe sanding or polishing step, it is also preferable to remove a smallamount of the ceramic surrounding support structure 29 or body of thedevice 10, for a very clean final appearance.

In yet another variation on the method depicted in FIGS. 26A-C, thevoids 45 may be created inside the edge of the device 10 during thebuild-up process, and only exposed to the edge after the device 10 issintered, to avoid the possibility of de-lamination. Stress duringsintering can pull at the edges of a multi-layer structure, and if astarter gap is present, a de-lamination can occur. Thus, as shown inFIG. 27, the gap-forming material may be used within ceramic layers toform internal voids 45 inside the device 10 near the edge, followed byexposing the voids 45 through a polish or removal process that removesthe ceramic surrounding support structure 29 to the dotted line. Thisensures that the device 10 has maximum strength through themanufacturing process. The steps of FIGS. 26A-C could then be performedto create the recessed contact pads 44.

FIGS. 28A-28D depict an embodiment for forming a device 10 that combinesthe concepts of FIGS. 24 and 26C, including how layers and gap-formingmaterial could be combined to form this structure, which includesconnecting in series the anode 24 of one active structure 50 to thecathode 26 of an adjacent active structure 50. In FIG. 28A, ceramiclayers for forming supporting structure 29, layers for anode 24 andcathode 26, and gap forming material layers 66 are assembled into agreen material stack, and the stack is laminated by applying pressure.The series of dots indicates the existence of additional layers thatform the remainder of each of the two active structures, but which areomitted in the depiction for visual simplicity. FIG. 28B schematicallyshows the side margin 56 of the structure after lamination. Heat is thenapplied to sinter the green materials, and then ceramic material fromlayers 29 is polished away from the side margin 56 to the dotted line.FIG. 28C depicts the structure after sinter and polishing off the edgematerial to expose the void 45. FIG. 28D depicts the device 10 aftermetallization and polishing away any excess metal to form the recessedcontact pad 44 that is bonded to the surface of each of the anode 24 andcathode 26 to form strong bonds between the electrodes and the seriesconnection metallization.

According to another embodiment, and as shown in FIG. 29, a stack ofdevices 10 is formed using a conductive metal felt 48, such as nickelfelt. In accordance with an embodiment, each device 10 has a surfaceconductor 44 on each of the top side and the bottom side, in the hotzone 32. One of these surface conductors 44 has positive polarity, andone has negative polarity. A plurality of these devices 10 is thenstacked together, forming a bundle that gives high total power. Theconductive metal felt 48 is placed between the positive terminal of onedevice and the negative terminal of the next device, thus linking thosetwo devices in series. Other metals can be used besides nickel,including copper, precious metals, or other non-noble metals. The use ofcertain metals such as nickel as the conductive metal felt 48 requiresthat the furnace 76 be operating in a reducing atmosphere; that is,there is a net fuel-rich atmosphere of such an extent that it preventsthe metal, such as nickel, from turning into metal oxide, such as nickeloxide. In addition, the surface conductors 44 between devices 10 neednot extend outside the furnace 76, whereas on the top and bottom devices10 in the stack, a conventional surface conductor 44 is present on thesurface to take electricity to the outside of the furnace 76. Anadvantage of using the conductive metal felt 48 is that the connectionbetween the devices 10 may have a lower resistance than if each device10 had connections that came to the outside of the furnace 76.Therefore, this technique can give lower system losses.

In providing high strength and integrity to the active structures 50 ofthe device 10, there are competing factors in the design considerations.One factor is that the electrolyte 28 is advantageously very thin, togive the best ion transport. Another factor is the thickness of theanodes 24 and cathodes 26. If they are too thin, then they may nottransportions or electrons well enough; but if they are too thick, theymay slow down gas transport, or they might cause mismatch problems withthe other materials in the device 10.

In accordance with one embodiment, depicted in partial cross-section inFIG. 30, porous ceramic 64, such as YSZ (or an equivalent), is added tothe top and bottom of the active structure 50 on the electrodes. Byusing this technique to add thickness to the active structure 50, itallows the electrolyte 28 to be made as thin as possible withoutweakening the overall active structure 50. In addition, it permitsoptimizing the thickness of the anode 24 or cathode 26 without regard toother considerations, such as strength of the overall structure. Also,without adding this extra ceramic, issues such as CTE (coefficient ofthermal expansion), shrinkage and overall compatibility of the threelayer active structure 50 (anode 24/electrolyte 28/cathode 26) would bedominated by the anode 24 and cathode 26, whereas this technique shiftsthe balance back toward the properties of the porous ceramic 64,assuming that the same type of ceramic, e.g., YSZ that is non-porous orporous, forms all or a portion of the bulk material that is used tocreate the surrounding support structure 29.

The porosity of the porous ceramic 64 is critical to the function of theactive structure 50, since it must allow transport of gas through thepores. The pores can be created by the use of pore-forming materials,various organic particles or fibers, as described above, such that anetwork of pores is created throughout the porous ceramic 64, as shownabove the anode 24. Also, the pores can be formed through the use of viapunching techniques, so that the pores are actually large, verticalopenings, as shown below the cathode 26. Also, the porous ceramic 64 canbe achieved by using calcined ceramic (e.g., YSZ) particles, or simplyvery large ceramic particles, such that they do not sinter well at thetemperatures used for sintering the overall device 10. Combinations ofthese methods can be used concurrently.

In some devices 10 of the invention, depending on the operating gasesand temperatures, it is possible that carbon buildup can occur in thegas passageways, for example, in the entry passages in the cold zone 30,in areas where reforming happens, or in the area of temperaturetransition, from cool to hot, i.e., the transition zone 31. Twosolutions to carbon buildup include providing an increased temperaturegradient at the entryway, temporarily, to clean out carbon, and/oraltering the gas composition, temporarily, in a cleaning step.

With the understanding that carbon can be effectively removed in air attemperatures that exceed a threshold temperature, but that below thethreshold temperature, it is possible that carbon can remain in ceramicstructures, it may be contemplated that carbon could build up in regionsof a device 10 where the transitional temperature of the device 10 isbelow the threshold temperature, such as in the wall of the furnace 76and/or the transition zone 31, while the hot zone 32 operates above thethreshold temperature. Thus, the hot zone 32 could be made to expand toa larger area that encompasses the transition zone 31 for a cleaningstep. In one embodiment, depicted schematically in FIG. 31, the furnace76 containing the device 10 has a double wall with an outer wall 77encompassing all or a portion of the transition zone 31 and the innerwall 78 encompassing the hot zone 32, with heating elements (not shown)placed between the two walls 77, 78. When the device 10 is operating infuel cell mode, the heating elements between walls 77, 78 are not turnedon, such that transition zone 31 operates as intended as the temperaturetransition area from cold to hot (and hot to cold). When the device 10is operated in cleaning mode, the heating elements are turned on to heatthe additional enclosed area above the threshold temperature to removeany carbon buildup, thereby cleaning passages outside the hot zone.

In another embodiment, the composition of the fuel gas stream that isentering the device can be modified to alter the ppm (parts per million)oxygen content in the fuel stream. The partial pressure of oxygen in thefuel stream, as measured in ppm, can be modified by adding water vaporto the fuel gas, for example. The stability balance between carbon andcarbon monoxide (C/CO) is dependent on the ppm of oxygen present, andthe temperature. By varying the temperature in the passages and/or byvarying the oxygen content, the equilibrium can be shifted to causecarbon to change to carbon monoxide. Similarly there is an equilibriumbetween Ni/NiO that is dependent on temperature and ppm of O₂, such thatthe modifications should be selected so as to not also change the nickelmetal into nickel oxide at the anode.

Finally, the entire device could be baked at high temperature on aperiodic basis to clean the internal passages. A device 10 will have anoptimal usage temperature, for example, 900° C., and a cleaning baketemperature may then be set above the optimal usage temperature, forexample, 1000° C. This higher temperature could be conducive to cleaningunwanted materials out of the device 10. However, precautions may beneeded prior to implementing a full-device bake, for example, removal ofany low temperature connections that might be compromised by the hightemperature bake.

For the cleaning operations described above, a control system couldperform the cleaning process automatically on some pre-determinedschedule, such as based on hours of operation or amount of powergenerated, or it could perform the process based on measurements takenin real time. The cleaning process could again combine one or both of achange in chemical composition of the incoming fuel stream or a changein temperature in all or part of the device.

While the invention has been illustrated by the description of one ormore embodiments thereof, and while the embodiments have been describedin considerable detail, they are not intended to restrict or in any waylimit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. The invention in its broader aspects is therefore not limited tothe specific details, representative apparatus and method andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the scope of thegeneral inventive concept.

What is claimed is:
 1. A fuel cell device, comprising: one or moreactive structures each having an anode and cathode in opposing relationwith an electrolyte therebetween; and a surrounding support structureincluding a top cover region, a bottom cover region, opposing sidemargin regions, and optional interposer layer regions, the surroundingsupport structure positioned in surrounding relation to the one or moreactive structures and being monolithic with one of the anode, cathode orelectrolyte of each of the one or more active structures, wherein amaterial composition used for the surrounding support structure includesa modification configured to alter the shrinkage properties of thesurrounding support structure to more closely match shrinkage propertiesof the one or more active structures than in the absence of themodification, said modification including one or more of the following:(a) where the surrounding support structure comprises a ceramic materialthat is monolithic with the electrolyte, the material compositionincludes an addition of anode or cathode material in one or more of theregions; (b) where the surrounding support structure comprises an anodematerial that is monolithic with the anode, the material compositionincludes an addition of electrolyte or cathode material in one or moreof the regions; (c) where the surrounding support structure comprises acathode material that is monolithic with the cathode, the materialcomposition includes an addition of electrolyte or anode material in oneor more of the regions; (d) an addition of an inorganic shrinkagecontrol material to the material composition that is not present in theone or more active structures; (e) an increase in particle size used forthe material composition than the particle sizes of materials used inthe one or more active structures; (f) a decrease in particle size usedfor the material composition than the particle sizes of materials usedin the one or more active structures; or (g) an addition of an organicfugitive material to the material composition that is not present in theone or more active structures or in an amount greater than present inthe one or more active structures, which organic fugitive material isremoved during baking and/or sintering of the material composition toform pores or voids in the surrounding support structure.
 2. The fuelcell device of claim 1, including modification (a), wherein the additionincludes alternating composite layers of anode material and cathodematerial, each mixed with electrolyte material.
 3. A fuel cell device,comprising: an active structure having an anode and cathode in opposingrelation with an electrolyte therebetween; an inactive surroundingsupport structure monolithic with the electrolyte and defining a firstportion of an outer surface of the device, wherein the inactivesurrounding support structure lacks the anode and cathode in opposingrelation and the active structure resides within the inactivesurrounding support structure with the anode exposed at a second portionof the outer surface and the cathode exposed at a third portion of theouter surface; a first surface conductor on the second portion of theouter surface in electrical contact with the exposed anode and extendingover the first portion of the outer surface; a second surface conductoron the third portion of the outer surface in electrical contact with theexposed cathode and extending over the first portion of the outersurface; a non-conductive, insulating barrier layer between the activestructure and the first and second surface conductors extending over thefirst portion.
 4. The fuel cell device of claim 3, wherein thenon-conductive, insulating barrier layer is a surface layer that liesbetween the first portion of the outer surface and the first and secondsurface conductors extending over the first portion.
 5. The fuel celldevice of claim 3, wherein the non-conductive, insulating barrier layeris an internal layer that lies within the surrounding support structurebetween the first portion of the outer surface over which the first andsecond surface conductors extend and the active structure.
 6. The fuelcell device of claim 3, wherein the non-conductive, insulating barrierlayer is glass or non-conducting ceramic.
 7. The fuel cell device ofclaim 3, further comprising an internal non-conductive passivation layeradjacent to one or both of the exposed anode and exposed cathode withinthe inactive surrounding support structure.
 8. A fuel cell system,comprising: a fuel cell device having first and second opposing endswith an elongate body therebetween comprising an active structure havingan anode and cathode in opposing relation with an electrolytetherebetween, and an inactive surrounding support structure monolithicwith the electrolyte and lacking the anode and cathode in opposingrelation, wherein the active structure resides within the inactivesurrounding support structure, and wherein the inactive surroundingsupport structure adjacent the first opposing end is larger in at leastone dimension relative to a remainder of the elongate body to form afirst enlarged attachment surface at the first opposing end; a heatsource for applying heat to the fuel cell device, wherein at least afirst portion of the elongate body containing the active structureresides within the heat source and at least a second portion of theelongate body including the first opposing end containing the firstenlarged attachment surface resides outside the heat source; and aninsulating material between the first and second portions of theelongate body shielding the first opposing end from the heat source. 9.The fuel cell system of claim 8, further comprising one or moreresistance heating elements on a surface of the portion of the elongatebody residing within the heat source and coupled to end contacts on asurface of the elongate body residing outside the heat source.
 10. Thefuel cell system of claim 8, wherein the inactive surrounding supportstructure adjacent the second opposing ends is larger in at least onedimension relative to the remainder of the elongate body to form asecond enlarged attachment surface at the second opposing end, and athird portion of the elongate body including the second opposing endcontaining the second enlarged attachment surface resides outside theheat source with the insulating material further between the first andthird portions of the elongate body shielding the second opposing endfrom the heat source.
 11. A fuel cell device comprising: first andsecond opposing ends defining an elongate body therebetween of lengthgreater than width and thickness, an active structure in the elongatebody having an anode and cathode in opposing relation with anelectrolyte therebetween, and an inactive surrounding support structuremonolithic with the electrolyte and lacking the anode and cathode inopposing relation, the active structure residing within the inactivesurrounding support structure, wherein the width of one or both of theanode and cathode progressively changes along the length of the elongatebody in the active structure.
 12. The fuel cell device of claim 11,wherein the width increases continuously.
 13. The fuel cell device ofclaim 11, wherein the active structure comprises a plurality of cellselectrically connected in series, each having the anode and cathode inopposing relation with the electrolyte therebetween, wherein the widthfor each cell progressively changes along the length.
 14. The fuel celldevice of claim 13, the width for each cell is greater than that of thepreceding cell.
 15. A fuel cell device, comprising: a multilayer activestructure having electrode layers in opposing relation with anelectrolyte therebetween, the electrode layers alternating in polarityfrom a top electrode layer to a bottom electrode layer; an inactivesurrounding support structure monolithic with the electrolyte anddefining an outer surface of the device including a top surface, abottom surface and opposing side surfaces, wherein the inactivesurrounding support structure lacks the electrode layers in opposingrelation and the active structure resides within the inactivesurrounding support structure with at least one electrode layer of eachpolarity exposed at one of the opposing side surfaces; a first surfaceconductor on the outer surface in electrical contact with the exposedelectrode layer of one polarity; a second surface conductor on the outersurface in electrical contact with the exposed electrode layer of theother polarity, wherein the first and second surface conductors areconfigured to have a designated polarity in use, wherein one or both ofthe first and second surface conductors extend onto the top or bottomsurface, and wherein the polarity of the top electrode layer is the sameas the designated polarity when one or both of the first and secondsurface conductors extend onto the top surface and the polarity of thebottom electrode layer is the same as the designated polarity when oneor both of the first and second surface conductors extend onto thebottom surface to prevent polarity mismatches between the surfaceconductors and the electrode layers within the inactive surroundingsupport structure.
 16. A fuel cell system comprising: a fuel cell devicehaving a length between opposing first and second ends that is thegreatest dimension whereby the device exhibits thermal expansion along adominant axis that is coextensive with the length, an active heatedregion along a first portion of the length, an inactive cold regionalong a second portion of the length adjacent one or both of theopposing first and second ends, an inactive transition region along athird portion of the length between the first portion and the secondportion, and an electrolyte disposed between an anode and a cathode inthe active heated region, wherein the anode and cathode each have anelectrical pathway extending to an exterior surface of the inactive coldregion for electrical connection; a double wall furnace comprising aninner wall and an outer wall, the inner wall defining an inner chambertherein and the outer wall defining an outer chamber, wherein the fuelcell device is positioned with the first portion of the length withinthe inner chamber, the third portion of the length within the outerchamber, and the second portion of the length outside the furnace; and afirst heating element coupled to the inner chamber for heating theactive heated region to a temperature above a threshold temperature fora fuel cell reaction to occur therein; a second heating element coupledto the outer chamber and operable to switch between an off positionwhere the inactive transition region has a temperature below thethreshold temperature when the active heated region is above thethreshold temperature and an on position where the inactive transitionregion has a temperature above the threshold temperature for cleaninggas passages within the inactive transition region; a control systemcoupled to the first and second heating elements and configured toswitch the second heating element between the off and on positions basedon one of a pre-determined cleaning schedule or a cleaning scheduletriggered by real time measurements.